Components of various industrial devices are often subjected to extreme conditions, such as high impact contact with abrasive surfaces. For example, such extreme conditions are commonly encountered during subterranean drilling for oil extraction or mining purposes. Diamond, with its unsurpassed wear resistance, is the most effective material for earth drilling and similar activities that subject components to extreme conditions. Diamond is exceptionally hard, conducts heat away from the point of contact with the abrasive surface, and may provide other benefits in such conditions.
Diamond in its polycrystalline form has added toughness as compared to single crystal diamond due to the random distribution of the diamond crystals, which avoids the particular planes of cleavage found in single diamond crystals. Therefore, polycrystalline diamond is frequently the preferred form of diamond in many drilling applications or other extreme conditions. A drill bit that utilizes this material is referred to as a PDC (Polycrystalline Diamond Cutter) bit. Polycrystalline diamond can be manufactured in a press by subjecting small grains of diamond and other starting materials to ultrahigh pressure and temperature conditions.
The manufacturing process for a traditional PDC is very exacting and expensive. The process is referred to as “growing” polycrystalline diamond directly onto a carbide substrate to form a polycrystalline diamond composite compact. The process involves placing a cemented carbide piece and diamond grains mixed with a catalyst binder into a container of a press and subjecting it to a press cycle using ultrahigh pressure and temperature conditions. The ultrahigh temperature and pressure are required for the small diamond grains to form into an integral polycrystalline diamond body. The resulting polycrystalline diamond body is also intimately bonded to the carbide piece, resulting in a composite compact in the form of a layer of polycrystalline diamond intimately bonded to a carbide substrate.
The composite compact allows the attachment of the polycrystalline diamond body to other materials via attachment of the bonded carbide substrate to those materials. Unlike polycrystalline diamond, carbide may be easily attached to other materials via conventional methods, such as soldering and brazing. These methods may be performed at relatively low temperatures at which the polycrystalline diamond portion of the composite compact remains stable.
A problem with polycrystalline diamond composite compacts arises from the use of cobalt or other metal catalyst/binder systems to facilitate polycrystalline diamond growth. After crystalline growth is complete, the catalyst/binder remains within pores of the polycrystalline structure. Because cobalt or other metal catalyst/binders have a higher coefficient of thermal expansion than diamond, when the composite compact is heated, e.g., during the brazing process by which the carbide portion is attached to another material, or during actual use, the metal catalyst/binder expands at a higher rate than the diamond. As a result, when the composite compact is subjected to temperatures above a critical level, the expanding catalyst/binder causes fractures throughout the polycrystalline diamond structure. These fractures weaken the polycrystalline diamond body and can ultimately lead to damage to or failure of the composite compact.
Today's polycrystalline diamond material is designed to withstand temperatures at which composite compacts in the form of cutters are brazed to a drill bit (even multiple times), but as bits have been improved and used to drill harder and more abrasive formations, the temperature at the working face of a cutter can significantly exceed the critical temperature.
A new generation of polycrystalline diamond has been developed that utilizes a leached zone of diamond at the working face of the cutter. The majority of the catalyst/binder in this zone has been depleted, most often by acid leaching methods. Examples of current leaching methods are provided in U.S. Pat. No. 4,224,380, U.S. Pat. No. 7,712,553, U.S. Pat. No. 6,544,308, U.S. 20060060392 and related patents or applications. This process renders the polycrystalline diamond body more thermally stable in the leached zone while leaving the remainder of the body to provide attachment to the carbide substrate. Fully leached bodies (referred to hereafter as “thermally stable diamond” or “TSD”) may also be created using these processes. However, such bodies lack a carbide substrate, making it difficult to attach them to other components. After the metal catalyst/binder has been removed from polycrystalline diamond to form TSD, the material is relatively non-wettable and its surface does not readily attach or adhere to other materials.
As a result of difficulties in attachment, attempts have been made to mechanically attach TSD bodies to substrates or bits. TSD bodies have previously primarily been used for surface set drill bits, where cutters made from the TSD bodies are generally small and may be embedded into the bit body by more than 50% to effect a mechanical “lock.” One such system is described in U.S. Pat. No. 4,602,691. These and other mechanical locking methods are described in U.S. Pat. No. 7,533,740, U.S. Pat. No. 4,780,274, U.S. Pat. No. 4,629,373 and related patents or applications, but such methods are prone to failure.
For instance, in U.S. Pat. No. 4,780,274, holes in a TSD body were filled with bit matrix. However, due to the low wetting capacity of TSD, the TSD elements were not effectively held by the bit matrix. Furthermore, because the bit body lacks the mechanical strength of cemented carbide or other substrate materials, TSD elements attached to a bit as disclosed in U.S. Pat. No. 4,780,274 are prone to failure under high load or impact.
Similarly, U.S. Pat. No. 4,629,373 discloses a TSD body with surface irregularities that are used in an attempt to mechanically lock the TSD to a substrate. However, the surface irregularities in U.S. Pat. No. 4,629,373 are not sufficient to achieve permanent attachment of the TSD and a substrate because the non-attachability of diamond to other materials is not overcome.
Other techniques seeking to avoid reliance on such mechanical trapping have centered around enhancements to the surface of the TSD that enable it to be brazed to a carbide substrate or carrier in much the same way a traditional polycrystalline diamond composite compact cutter is brazed to a bit. Example brazing methods are described in described in U.S. Pat. No. 4,850,523, U.S. Pat. No. 7,487,849, U.S. Pat. No. 4,225,322 and related patents or applications. Although some level of success has been reported with such techniques, commercial products employing them are not yet available.
Accordingly a need exists for methods of reliably attaching TSD to a substrate, in particular a substrate that will allow the ultimate attachment of the TSD via conventional methods such as brazing or soldering to drill bits or other components used in extreme conditions where TSD is beneficial.